1. Field of the Invention
This invention relates to a method for making molded photointerrupters. The present invention also relates to an apparatus for making molded photointerrupters.
2. Description of the Prior Art
As is well known, a photointerrupter is a photoelectric device which include a light emitting device (e.g. light emitting diode) and a light receiving device (e.g. phototransistor or photodiode) opposed to the light emitting device with a certain clearance. A detection signal is generated when an object interrupts the optical path between the two photo devices in the clearance. Such a photointerrupter is disclosed in Japanese Patent Application Laid-open No. 60-113480, Japanese Utility Model Application Laid-open No. 55-181359 and Japanese Utility Model Application Laid-open No. 57-94965 for example.
For the convenience of the following description, reference is now made to FIGS. 14-16 which show a typical prior art photointerrupter.
As shown in FIGS. 14 and 15, the prior art photointerrupter denoted by reference sign PI comprises a light emitting device L1 having a pair of leads P1a, P1b, and a light receiving device L2 also having a pair of leads P2a, P2b. The two photo devices L1, L2 are opposed to each other with a certain clearance, and integrated together by a molded package M made of non-transparent resin.
As shown in FIG. 16, the light emitting device L1 includes a light emitting semiconductor chip C1 mounted on one lead P1b and connected to the other lead P1a by a wire W1. The semiconductor chip C1 together with the wire W1 is enclosed in a molded sub-package M1 made of transparent resin.
As shown in FIG. 17, the light receiving device L2 includes a light receiving semiconductor chip C2 mounted on one lead P2b and connected to the other lead P2a by a wire W2. The semiconductor chip C2 together with the wire W2 is enclosed in a molded sub-package M2 made of transparent resin.
In manufacture, use is made of two leadframes which include a first leadframe A1 carrying pairs of leads P1a, P1b, and a second leadframe A2 also carrying pairs of leads P2a, P2b, as shown in FIG. 18. The respective leadframes A1, A2 are vertically oriented and transferred in parallel to each other by utilizing respective feed holes F1, F2. During transfer, light emitting devices L1 are made for the respective pairs of leads P1a, P1b of the first leadframe A1, whereas light receiving devices L2 are made for the respective pairs of leads P2a, P2b of the second leadframe A2. Then, resinous molded packages M are formed for the respective pairs of photo devices L1, L2, as shown in FIGS. 18 and 19.
FIG. 20 shows a mold which has been conventionally used for forming resinous molded packages M. Specifically, the mold includes a fixed lower mold member 111, a vertically movable upper mold member 112, and a pair of side mold members 113, 114 movable laterally toward and away from each other between the lower and upper mold members 111, 112. The respective mold members 111-114 define a plurality of molding cavities 115 (only one shown) when the mold is closed.
The lower mold member 111 has upward projections 116 associated with each molding cavity 115, and a corresponding pair of photo devices L1, L2 of the two leadframes A1, A2 are made to rest on the respective upward projections 116. The lower mold member further has an ejector pin 117 for pushing up a corresponding molded package M together with the respective leadframes A1, A2 upon opening of the mold.
The upper mold member 112 has a spacer projection 118 associated with each molding cavity 115. When the mold is closed, a corresponding pair of photo devices L1, L2 are held in contact with the spacer projection 118 on both sides thereof. The upper mold member 112 is also provided with gates 119 for injecting fluid resin into the corresponding molding cavity 115.
The respective side mold members 113 have backup projections 120a, 120b associated with each molding cavity 115 for pressing the corresponding pair of photo devices L1, L2 into contact with the corresponding spacer projection 118 when the mold is closed.
The prior art mold shown in FIG. 20 is disadvantageous in the following points.
First, because of the vertical arrangement of the respective leadframes A1, A2 within the mold, the clearance between the lower mold member 111 and each side mold member 113, 114 should be as narrow as possible in order for the respective photo devices L1, L2 to reliably rest on the respective upward projections 116 at the time of introducing the leadframe into the mold. However, it is difficult or relatively time-taking to insert the leadframe in such a narrow clearance. Thus, the prior art mold is not suitable for complete automation of the molding operation, thereby resulting in a cost increase.
Secondly, since each pair of photo devices L1, L2 must rest on the corresponding upward projections 116 during the molding operation, it is inevitable that corresponding holes are formed in the subsequently obtained molded package M. Obviously, the presence of such holes reduces the value of the product. Further, the provision of the upward projections 116 complicates the structure of the mold, resulting in an additional cost increase.